Jonathan, Kiki, anyone? Need help on a mixed mono setup

[Fishy]

Hey guys.

I'm trying to help out a guy on the ecoustics forum wire one 12 ohm and two 8 ohm subs to what appears to be an RF 800a2. I know. Big cluster$%#@, but I think I came up with a mixed mono solution that should work half decent anyways.

http://forum.ecoustics.com/bbs/messages/4/138863.html

If someone who's familiar with 3 channel operation of 2 channel amps could verify that I'm giving good advice I'd appreciate it.

thanks

-Fishy

[Jonathan]

He could always wire 4 ohm resistors in series with the two 8 ohm drivers, and connect them all to the amplifier for a final 4 ohm bridge. Impedance won't be totally correct, but much more so than mixing those drivers.

[71buickfreak]

the complexity of that set up isn't worth the time. Why does he have to run 3 subs? I would tell him this really isn't a good plan, it would sound better with just the 2 8-ohm subs, since it won't have the third 12-ohm sub robbing power from the other 2. Please tell me this isn't going in the same box with out dividers. is it possible to hook them up and get them to work? yes. Is it really a viable option? no, its a waste of time. Are they even the same brand and model? Just because he has 3 subs doesn't mean he needs to use them. explain to him that by running the third sub, he will not only be lowering the power output of the amp, he will be making his system less loud than if he were to run the 2 8-ohms subs. explain to him that by adding the 12 ohm sub while adding an additional 1\3 cone area (which would only yield about 1 db theoretically), he will be adding more resitance to the amplifier (not to mention back-EMF, which effects the damping factor and sound quality of the system) which will lower the power output and decrease his volume more than the 1 db he would have gained by adding the 3rd sub. If he must have this 3rd sub, he needs to sell or trade it for a unit that is the same brand and model of his other 2 in the same ohm configuration. anything else is just a waste of time and effort. remember, more is not always better. I just checked your thread over there. I see the situation now. DO NOT RUN THE MP WITH 1 CHANNEL TO 1 SUB AND THE 2 ON THE OTHER! That will create an uneven load on the amp and eventually burn it up. they aren't designed to work like that. also, with an 800.2, there are only 2 rca inputs, not 4, the other to you would see in a picture are pass-through outputs. And 267 watts is nothing to these subs, not a problem to run that much power as long as it is properly set up. I have run 1000 watts to a single 12 w0 before with no probs. As far as the extra power going to the single 12-ohm sub, no worries there as the higher load vc will eat a lot of that power, it may not even play as loud as the other two, especially if he did that 1 channel on 1 and 1 channel on 2 subs. there's my nickels worth on a pennies budget. let me know what happens.

[Jonathan]

You wouldn't increase the resistance to the amp by adding a 12 ohm sub in parallel, it would still lower. 1/12 + 1/8 + 1/8 = 1/Rt, which would be a final load of 3 ohms, opposed to 4 ohms for only running the dual 8 ohm subs. I agree though, he'd get better results just worrying about the two subs and focusing on making the most out of those.

[Jonathan]

Of course, that's assuming a single channel bridge, which would be pushing it with a 3 ohm load.

[Fishy]

How could it be the same as the amp seeing a 3 ohm bridged load if the total output is merely 467 watts with an 800 watt capable amplifier? With the mixed mono configuration he'd be combining two 8 ohm stereo loads(100w each) with a 12 ohm bridged load(267w).

That just happens to be the same total power output as if he bridged the amp into a 6.86 ohm load, i.e. the two 8 ohm subs combined in series, then in parallel with the 12 ohm driver.

Req = 1/(1/(8+8) + 1/12) = 1/(1/16 + 1/12) = 6.86.

and if P(4) = V^2/R = 800w with R = 4 ohms then P(6.86) = 4*800/6.86 = 467 watts.

Sure its a ridiculous setup, but I'd think it would actually be simpler to wire up the subs in mixed mono than actually bridging the amp into that series/parallel combo. Unless I've misunderstood the way mixed mono works he'd also be avoiding the phase shift problems associated with wiring the two 12w0-8's in series.

I recommended that he ditch those subs and get three 12w3-d6's, but if he's broke he could run what he has like that until he gets enough cash for the d6's. Even 3 12w6 original or AE series would work if the enclosure isn't to big. His best bet would probably be a new enclosure with a pair of 12w6v2's although we're talking even more money now.

Doesn't matter. I probably scared the hell out of him with all that technical mumbo jumbo. He's probably sellin those subs and box as we speak, or beatin up the guy that sold him the stuff to begin with.

-Fishy

[Jonathan]

Situation where there's more than one way to skin a cat, and none of them will do the job well :)

[Fishy]

DO NOT RUN THE MP WITH 1 CHANNEL TO 1 SUB AND THE 2 ON THE OTHER! That will create an uneven load on the amp and eventually burn it up. they aren't designed to work like that. also, with an 800.2, there are only 2 rca inputs, not 4, the other to you would see in a picture are pass-through outputs. And 267 watts is nothing to these subs, not a problem to run that much power as long as it is properly set up. I have run 1000 watts to a single 12 w0 before with no probs.

Hmm.... I guess i probably ought to go tell him not to run an unbalanced load like that and I must've been reading the 800a4 suggestions and thinking about y-adapters.

With regards to to running 267w or even 1000w to a 12w0, I wouldn't have a problem either, but do you think this guy actually has a clue about not using a bunch of bass boost or maxing out the volume? much less setting the gains correctly? I dunno I find it hard to recommend more than twice the rated power for a sub to a newbie regardless if its a JL or not.

-Fishy

[Fishy]

Situation where there's more than one way to skin a cat, and none of them will do the job well :)

Lol, like I said. One big clusterfook.

I better go over there and tell him not to run that unbalanced thing.

-Fishy

[Fishy]

Oh, and thanks for checking my work. Believe me it took awhile to figure his situation out.

-Fishy